Biocompatible ceramics such as hydroxyapatite have high biocompatibility; hence, metals and ceramics coated with hydroxyapatite are excellent biomaterials. It has been confirmed that the propagation and/or differentiation of cells can be promoted in such a manner that the cells are cultured on substrates of these materials (see Patent Document 1). Sheets coated with the biocompatible ceramics have high abilities to adsorb biologically relevant substances and therefore have been investigated for use as isolation/analysis sheets for nucleic acids, proteins, and the like (see Patent Documents 2 and 3). Furthermore, there are transparent strips which are used to directly observe living cells and which are prepared by grinding a bulk of biocompatible ceramics sintered at high temperatures.
In addition to these sheets, a high bioadherence cultured cell sheet laminated on a porous film made from a hydrophobic organic solvent solution containing a biodegradable polymer and an amphipatic polymer (see Patent Document 4) or fibrous film, and a layered sheet of such high bioadherence cultured cell sheet (see Patent Document 5) are known hitherto.
Substrates coated with biocompatible ceramics are non-flexible and therefore are limited in working range. Cells cultured on the coatings cannot be collected such that tissues composed of the cells perform desired functions. Any cell sheets that are absorbed in living organisms after transplantation cannot be prepared. Since metal and ceramic substrates are opaque, it is impossible to observe the behavior, such as adhesion or differentiation, of living cells in real time.
The biocompatible ceramic-coated sheets can adsorb the biologically relevant substances or can be used to isolate the biologically relevant substances but cannot be used to observe the interaction between the biologically relevant substances in real time because these sheets are opaque.
Further, there is a limitation on thinning the bulk of biocompatible ceramics by grinding; hence, any transparent strips which are flexible and soft cannot be obtained from the bulk biocompatible ceramics. Therefore, such transparent strips cannot be used as coating materials for tissues, such as soft tissues, required to be soft.
In addition, the porous film contains a synthetic resin of amphiphatic polymer and therefore may be biologically toxic. The high bioadherence cell culturing sheet contains the fibrin gel and therefore may cause viral infections.    Patent Document 1: Laid Open Japanese Patent Application Publication (Unexamined) No. 278609/2005    Patent Document 2: Laid Open Japanese Patent Application Publication (Unexamined) No. 88819/1995    Patent Document 3: Laid Open Japanese Patent Application Publication (Unexamined) No. 156814/1998    Patent Document 4: Laid Open Japanese Patent Application Publication (Unexamined) No. 157574/2001    Patent Document 5: Laid Open Japanese Patent Application Publication (Unexamined No. 00608/2005